Bake the cake mix according to package directions using a 13x9 inch pan at 325°F. The lower temperature will help prevent the cake from doming. Let the cake cool completely.
Once the cake is cool, beat the butter, crisco, sugar, vanilla, and evaporated milk in a stand mixer on high for 15 minutes. The mixture will be light and fluffy. Spread over cooled cake.
Remove the lid from the frosting can. Remove the foil seal completely (see notes if the foil doesn’t come off completely). Place the can of frosting in the microwave for 15 seconds. Stir and microwave for an additional 15 seconds or until the frosting is pourable.
Pour the frosting over the cream layer, and spread into an even layer. Let sit at room temperature until the frosting hards (about 2–3 hours) or refrigerate for 45 minutes. Cut into slices and serve.
If any portion of the foil seal is still on the frosting can, scoop the frosting into a microwave-safe bowl before microwaving. Foil cannot go in the microwave!